Publications with full text files / Publikationen mit Volltext(dateien) https://hdl.handle.net/20.500.12738/2 2026-06-18T00:24:45Z 2026-06-18T00:24:45Z Hoppen, Hannah https://hdl.handle.net/20.500.12738/19175 2026-06-17T13:36:53Z 2026-06-17T13:17:56Z

Title: Helmholtz resonators with integrated vibrating cantilevers for low-frequency noise control in aircraft sidewalls Authors: Hoppen, Hannah Abstract: For more efficient aircraft engines, the trend is toward larger bypass ratios and gear-driven fans or counter-rotating open-rotor engines. As a result, engine noise emissions will change to include not only broadband noise, but also discrete frequencies with high sound pressure levels in the low-frequency range. The current aircraft sidewall can be considered acoustically as a double wall consisting of the outer fuselage skin and the inner cabin lining with insulation material sandwiched in between these layers. This is a sufficient sound barrier in the high-frequency range i.e. above 1000 Hz, but in the low-frequency range, where a number of tones from the future aircraft engines are expected, the sound insulation is less effective in reducing noise. Due to lightweight aircraft design principles, better sound insulation cannot be achieved by increasing the double wall mass or spacing. Therefore, there is a need for a new concept of an aircraft sidewall with improved low-frequency sound insulation that does not notably increase the weight or space constraints of the conventional wall. To address this challenge, this work presents a novel Helmholtz resonator type with two resonance frequencies integrated into an aircraft-like double wall to improve the sound transmission loss over a broader frequency spectrum, especially in the low-frequency range. The resonator incorporates a U-shaped slit that forms a cantilever. This cantilever provides a second resonance frequency, effectively broadening the frequency range with significant noise reduction. Constructed of a lightweight closed-cell foam, the resonator maintains its weight and volume compared to conventional Helmholtz resonators, offering a distinct advantage over the Helmholtz resonators with two resonance frequencies presented in the current literature. In addition, an analytical model for the Helmholtz resonator with integrated cantilever is developed in this thesis. This model allows an accurate determination of resonance frequencies and an evaluation of the absorption and transmission behavior. Furthermore, the model is verified and validated by finite element simulations and experiments, respectively, and extended to analyze multi-layer structures using the transfer matrix method. Parameter studies based on these analytical models are used to identify tuning mechanisms of the resonance frequencies and geometry parameters that influence the noise reduction behavior of the resonator. Optimization calculations were carried out to design a resonator panel that, when integrated into the aircraft sidewall, expands the frequency range of increased transmission loss in the low-frequency domain. This sound insulation improvement was successfully demonstrated in a laboratory test setup.

2026-06-17T13:17:56Z Münch, Lukas Rose, Philip Erdmann, Patrick Linke, Markus Middendorf, Peter https://hdl.handle.net/20.500.12738/19376 2026-05-28T00:08:15Z 2026-05-26T13:18:41Z

Title: Fatigue life of a single lap joint with and without special events Authors: Münch, Lukas; Rose, Philip; Erdmann, Patrick; Linke, Markus; Middendorf, Peter Abstract: The development of fatigue-resistant adhesive joints and adjacent parts remains challenging, particularly when simulating crack propagation under fatigue loading. Commercial software packages, such as ABQUS, include cohesive zone elements; however, they usually require user-defined subroutines for fatigue applications. This study combines multiple subroutines to predict the crack path across multiple lamina layers originating from a pre-crack. The interlaminar/adhesive subroutine employs a userdefined material model to assess cohesive stress and damage in the joint [1]. Additionally, a second user-defined subroutine developed at HAW Hamburg was used for intralaminar damage. Both subroutines were incorporated into the FEM software ABAQUS to enable information exchange between material models [2]. This allows the initiation of delamination from the matrix damage, in addition to a crack propagating through the lamina. The evaluation was conducted on a specimen measuring 100 mm × 150 mm, including a single-lap bonded joint. The specimens were subjected to cyclic tension at an R ratio of 0.1. For the impact assessment, a custom mapper developed by Wölfel was used to map the initial damage based on separate impact simulation results, enabling a distinct analysis method for fatigue. Using this method, a validated tool for predicting the fatigue life of a bonded joint was presented. [1] L. F. Kawashita and S. R. Hallett, "A crack tip tracking algorithm for cohesive interface element analysis of fatigue delamination propagation in composite materials," International Journal of Solids and Structures no. 49, pp. 2898-2913, 2012. [2] R. Sachse, A. Pickett, M. Käß and P. Middendorf, "Numerical Simulation of Fatigue crack growth in the Adhesive Bondline of hybrid CFRP Joints," in COMPOSITES, Bristol, 2015.

2026-05-26T13:18:41Z Rose, Philip Körwien, Thomas https://hdl.handle.net/20.500.12738/16820 2026-05-28T00:00:34Z 2026-05-26T12:51:26Z

Title: Investigations on the influence of design parameters on the strength of CFRP repairs Authors: Rose, Philip; Körwien, Thomas Abstract: Traditional repair methods involving riveted joints necessitate the creation of numerous holes in still-intact material, thereby compromising the structural integrity of the area. Load transmission between the adherents occurs within this weakened zone. This disadvantage can be avoided through adhesive-based repairs. Presently, aviation authorities only certify the use of bonded repairs for very small areas of damage. For the experimental investigation of bonded repairs, a standardized specimen at the coupon level, the EN6066 specimen, is available. However, this specimen represents a considerable simplification compared to actual repairs. Therefore, effects that have a significant influence may no longer occur, or only to a small extent, when they are analysed on more realistic specimens. In this study, "Cupped" and "Straight" repair configurations, differing in the arrangement of repair plies, were experimentally tested at both coupon and element levels under quasi-static loading. Significant variations were observed, strength differences between Cupped and Straight at the coupon level vary by about 27%, whereas the configurations exhibited only a 2% strength difference when tested at the element level. These disparities primarily are caused by the distinct detailing of the represented repair geometry, illustrating the challenges associated with designing specimens for investigating repair methods.

2026-05-26T12:51:26Z Kernstock, Paul Lorenzen, Peter Tillmann, Philip Schäfers, Hans https://hdl.handle.net/20.500.12738/19004 2026-04-30T07:50:32Z 2026-04-28T14:32:49Z

Title: Jarvis – ein verteilter Simulator für hoch aufgelöste Systeme des Energiesektors Authors: Kernstock, Paul; Lorenzen, Peter; Tillmann, Philip; Schäfers, Hans Abstract: Heutige Anwendungsfälle der technischen Modellierung und Simulation für gekoppelte Energieversorgungssysteme, insbesondere Wärmeversorgungssysteme, stellen hohe Anforderungen an die Performanz von Simulatoren. Dieses Paper stellt eine neue Architektur für die Modellierung und verteilte Simulation dieser technischen Systeme vor. Der hybride Ansatz kombiniert gleichungsbasierte und Objekt-orientierte Modellierung mit ereignisbasierter verteilter Simulation. Auf Grundlage der spezifischen Struktur eines Modells bietet der Ansatz die Möglichkeit, verteilbare und nicht verteilbare (monolithische) Teile zu separieren und die Berechnung damit effektiv auf Multicore-Rechner und Rechencluster zu verteilen und somit performante Berechnungen durchzuführen. Das Paper stellt die Struktur der Architektur, die Funktionalitäten des Simulators sowie die informationstechnische Infrastruktur im Detail vor, die die verteilte Simulation ermöglichen. Anhand der Berechnung thermo-hydraulischer Modelle, wie sie für Wärmeversorgungsnetze genutzt werden, wird die verteilte Simulation mit dem beschriebenen Ansatz veranschaulicht und erklärt.

2026-04-28T14:32:49Z